The proposed research seeks to understand how an organism's ecology and social environment influence the design of its animal communication signals and sensory receptors. Electrical communication is the model system. Current field research has shown that Mormyrid fishes of Gabon West Africa utilize electric communication in a variety of social roles including identification, aggregation, and dispersal. Electrolocation of objects functions concurrently. Correlations between a species' ecology, its spacing patterns, and its social environment with its mode of signaling, provide essential data for understanding signal evolution. Continuing research will emphasize (1) experimental evaluation of stimulus parameters that evoke identification responses of courting male Mormyrids (2) social signaling of Mormyrids (3) ecology of Mormyrids, and (4) geographic variability of electric signals in fish. In addition, laboratory research will continue on studies of stimulus filtering by peripheral electroreceptors of Gymnotoid and Mormyrid fishes. Electroreceptors of fish with distinctive electric signals will be compared. Stimulus filtering will be examined using "complex" stimuli which are distorted or altered in graded sequences. Plasticity of stimulus filtering will be explored.